JP7231445B2 - Water-based ink for inkjet printing - Google Patents

Description

The present invention relates to a water-based ink for inkjet printing and an inkjet printing method using the same.

The inkjet printing method is a printing method in which ink droplets are directly ejected from fine nozzles and adhered to a printing medium to obtain a printed material or the like on which characters or images are printed. This method has many advantages such as easy full-color printing, low cost, and non-contact with the printing medium, and is therefore becoming very popular. In recent years, in particular, from the viewpoint of weather resistance and water resistance of printed matter, the use of pigments as colorants has become mainstream.

By the way, flexible packaging for packaging foods and the like and label/sticker printing are widely used. In printing on flexible packaging and labels/stickers, printing is performed to indicate the name of the product to be packaged and attached to a thin, flexible, low-absorption printing medium made of synthetic resin or the like. Gravure printing is mainly used for such flexible packaging and label/sticker printing, but since gravure ink usually disperses or dissolves pigments and resins in an organic solvent, it does not affect the work environment. There's a problem.
Inkjet printing methods using energy ray-curable inks are also being studied for soft packaging printing and label/sticker printing. However, energy ray-curable inks have concerns about odor. In particular, since flexible packaging is often used for food packaging, the impact of this problem is increasing.

For this reason, the development of water-based inks for inkjet printing that imposes less burden on the working environment is underway.
For example, Patent Document 1 discloses an ink composition containing a colorant, an aqueous solvent, and a specific acetylene glycol-based surfactant as an ink composition that causes less foaming and enables stable printing by inkjet printing. .
Patent Document 2 describes pigments, water-insoluble polymers, The ink contains an organic solvent and a silicone surfactant, the organic solvent contains at least a glycol ether having a specific viscosity and vapor pressure, and the content of the organic solvent having a boiling point of 250° C. or higher in the ink is 5% by mass or less. , discloses water-based inks for inkjet recording.
In Patent Document 3, a water-based ink for inkjet recording that maintains the redispersibility of dried ink in an ink discharge nozzle and has excellent storage stability contains crosslinked polymer particles containing a pigment and a water-soluble amine compound. and a water-soluble organic solvent having a boiling point of 90 to 250° C., wherein the cross-linked polymer has a cross-linked structure containing a carboxy group and an ester group derived from a cross-linking agent, and a specific A water-based ink is disclosed having a saponification number of .

JP-A-2000-144026 JP 2017-8319 A Japanese Patent Application Laid-Open No. 2018-28080

For flexible packaging, etc., it is necessary to print product information such as product names and package inserts. However, if it becomes impossible to take time for drying due to a further increase in speed, troubles due to tackiness will occur when the printed matter is wound with roll paper or the like, or when the printed matter is piled up with sheets.
Here, the tackiness means adhesiveness such as stickiness (tackiness), and for example, it means that the printed portion is transferred and adheres to the back surface of the print medium, and the print medium becomes dirty. Accordingly, "high tackiness" means a large transfer smudge area, and "small tackiness" means a small transfer smudge area.
The present invention provides a water-based ink for inkjet recording, which is excellent in ejection stability and capable of obtaining printed matter with improved tackiness even on low liquid-absorbing printing media, and an inkjet printing method using the same. is the subject.

The present inventors used a silicone-based surfactant as a surfactant in a water-based ink containing a pigment, a water-soluble organic solvent, and a surfactant, and used propylene glycol (S1) and glycol ether as the water-soluble organic solvent. (S2) is used, the content of the solvent (S1) is less than 20% by mass, and the mass ratio of the solvent [(S2)/(S1)] is set to a specific range to solve the above problems. Found it.

That is, the present invention provides the following [1] and [2].
[1] A water-based ink for inkjet printing on a low-absorption print medium,
Contains a pigment, a water-soluble organic solvent, and a silicone surfactant,
The water-soluble organic solvent contains propylene glycol (S1) and glycol ether (S2),
The content of propylene glycol (S1) in the ink is less than 20% by mass,
the total content of the propylene glycol (S1) and the glycol ether (S2) in the ink is 4% by mass or more and 25% by mass or less;
mass ratio [(S2)/(S1)] of the glycol ether (S2) to the propylene glycol (S1) is 0.1 or more and 0.6 or less;
Viscosity at 32 ° C. is 2 mPa s or more and less than 5 mPa s,
Water-based ink for inkjet printing.
[2] An inkjet printing method, wherein the ink described in [1] is used to print on a low-absorbing print medium.

ADVANTAGE OF THE INVENTION According to the present invention, a water-based ink for inkjet recording, which is excellent in ejection stability and capable of obtaining a printed matter with improved tackiness even on a low liquid-absorption printing medium, and an inkjet printing method using the same are provided. can do.

[Water-based inkjet ink for printing on low-absorption printing media]
The water-based ink of the present invention is a water-based ink for inkjet printing on low-absorption printing media (hereinafter also referred to as "the ink of the present invention"),
containing a pigment, a water-soluble organic solvent, and a silicone-based surfactant, wherein the water-soluble organic solvent contains propylene glycol (S1) and glycol ether (S2);
The content of propylene glycol (S1) in the ink is less than 20% by mass,
the total content of the propylene glycol (S1) and the glycol ether (S2) in the ink is 4% by mass or more and 25% by mass or less;
mass ratio [(S2)/(S1)] of the glycol ether (S2) to the propylene glycol (S1) is 0.1 or more and 0.6 or less;
The viscosity at 32°C is 2 mPa·s or more and less than 5 mPa·s.
The term "aqueous" means that water accounts for the maximum proportion in the medium.
"Low liquid absorbency" is a concept including low liquid absorbency and non-absorbency of ink. Low liquid absorbency can be evaluated by pure water absorbency. More specifically, it means that the water absorption amount per surface area of the print medium is 0 g/m ² or more and 10 g/m ² or less when the print medium is in contact with pure water for 100 msec.
"Printing" is a concept that includes printing for recording characters and images.

According to the ink of the present invention, both ejection stability and tackiness can be improved. Although the reason is not clear, it is considered as follows.
In the present invention, the water-soluble organic solvent in the ink contains propylene glycol (S1) and glycol ether (S2) in a specific mass ratio. In addition, by setting the ratio of propylene glycol (S1) to less than 20% by mass with respect to the entire ink, the evaporation of water from the ink nozzle is suppressed, and after printing, the solvent can be quickly volatilized by heating, thereby minimizing the A strong ink film can be formed by the drying process, and adhesion between the print surface and the back surface of the print medium can be suppressed. Further, since the silicone-based surfactant is contained, together with the solvents (S1) and (S2), the ink surface of the ink nozzle can be maintained in an appropriate form, and a printed matter with excellent ejection stability can be obtained. It is considered possible.
In addition, by setting the total content of the solvents (S1) and (S2) to 4% by mass or more and 25% by mass or less with respect to the entire ink, the ink liquid surface of the ink nozzle can be maintained in an appropriate form, and after printing, Since the solvent can be volatilized quickly by heating, it is thought that deterioration of tackiness can be suppressed.

<Pigment>
Pigments used in the present invention may be either inorganic pigments or organic pigments, and lake pigments and fluorescent pigments may also be used. In addition, if necessary, they can be used in combination with an extender pigment.
Specific examples of inorganic pigments include metal oxides such as carbon black, titanium oxide, iron oxide, red iron oxide and chromium oxide, and pearl luster pigments. Carbon black is particularly preferred for black ink. Examples of carbon black include furnace black, thermal lamp black, acetylene black, channel black and the like.
Specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; Examples include polycyclic pigments such as linone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments.
The hue is not particularly limited, and achromatic pigments such as white, black and gray; and chromatic pigments such as yellow, magenta, cyan, blue, red, orange and green can be used.
Examples of extender pigments include silica, calcium carbonate, and talc.
The pigments may be used alone or in combination of two or more.

Preferred forms of the pigment used in the present invention include self-dispersing pigment particles and pigment particles containing a pigment in a polymer-type dispersant. Polymer particles containing pigments are preferred.
As used herein, the term “pigment-containing polymer particles” refers to a form in which a polymer-type dispersant contains a pigment, a form in which a part of the pigment is exposed on the surface of particles composed of a polymer-type dispersant and a pigment, and a polymer-type dispersant. It includes particles such as a form in which a dispersant is partially adsorbed on a pigment.
In the present invention, the pigment-containing polymer particles maintain a dispersed state with a particle diameter of 200 nm or less in the ink of the present invention.

(Polymer-type dispersant)
A polymer-type dispersant has the ability to disperse a pigment in a medium containing water as a main component, and is used as one component that constitutes the pigment-containing polymer particles. The polymer constituting the polymeric dispersant may be either a water-soluble polymer or a water-insoluble polymer, but a water-insoluble polymer is more preferred.
As used herein, the term "water-insoluble polymer" refers to a polymer that has reached a constant weight after being dried at 105°C for 2 hours, and dissolved in 100 g of water at 25°C until it is saturated, and the amount dissolved is less than 10 g. The amount dissolved is preferably 5 g or less, more preferably 1 g or less. When the polymeric dispersant is an anionic polymer, the dissolution amount is the dissolution amount when the anionic groups of the polymer are 100% neutralized with sodium hydroxide.

Polymer-type dispersants include vinyl-based polymers, polyester-based polymers, polyurethane-based polymers, and the like. Among these, vinyl-based polymers are preferred.
The polymeric dispersant preferably has ionic groups. The ionic group of the polymer-type dispersant is introduced into the polymer skeleton constituting the polymer-type dispersant by the ionic monomer (a-1) from the viewpoint of improving the dispersion stability and storage stability of the pigment-containing polymer particles. What is done is preferable.
Also, the polymeric dispersant preferably has a hydrophobic group. From the same viewpoint as above, the hydrophobic group of the polymeric dispersant is preferably introduced into the polymer skeleton constituting the polymeric dispersant by the monomer (a-2) having hydrophobicity.
That is, in the present invention, the polymeric dispersant is more preferably a vinyl polymer obtained by copolymerizing raw material monomers (a) containing an ionic monomer (a-1) and a hydrophobic monomer (a-2).
The polymer-type dispersant can further have a nonionic group from the same viewpoint as above. The nonionic group of the polymeric dispersant can be introduced into the polymer skeleton constituting the polymeric dispersant by the nonionic monomer (a-3).

[Ionic Monomer (a-1)]
The ionic monomer (a-1) includes anionic monomers and cationic monomers, preferably anionic monomers, more preferably acid group-containing monomers, and still more preferably carboxyl group-containing monomers.
Specific examples of the ionic monomer (a-1) include those described in paragraph [0017] of JP-A-2018-80255. Among them, (meth)acrylic acid is preferred.
In the present invention, the ionic groups introduced into the polymeric dispersant by the ionic monomer (a-1) are partially or wholly neutralized when forming the pigment-containing polymer particles. preferable.

[Hydrophobic monomer (a-2)]
As used herein, the “hydrophobicity” of the hydrophobic monomer (a-2) means that the amount dissolved in 100 g of ion-exchanged water at 25° C. until saturation is less than 10 g. . The dissolved amount of the hydrophobic monomer (a-2) is preferably 5 g or less, more preferably 1 g or less, from the viewpoint of fixability to the pigment.

The hydrophobic monomer (a-2) is preferably one or more selected from alkyl (meth)acrylates, aromatic ring-containing monomers and macromonomers, more preferably one or more selected from aromatic ring-containing monomers and macromonomers.
Specific examples of the hydrophobic monomer (a-2) include those described in paragraph [0018] of JP-A-2018-80255. Among these, one or more selected from styrene, α-methylstyrene and styrene macromers are preferred.

[Nonionic monomer (a-3)]
As the nonionic monomer (a-3), one or more selected from hydroxyalkyl (meth)acrylates, polyalkyleneglycol (meth)acrylates, alkoxypolyalkyleneglycol (meth)acrylates, and phenoxypolyalkyleneglycol (meth)acrylates. preferable.
Specific examples of the nonionic monomer (a-3) include those described in paragraph [0022] of JP-A-2018-80255. Among them, one or more selected from polypropylene glycol (n=2 to 30) (meth)acrylate and phenoxy (ethylene glycol/propylene glycol copolymerization) (meth)acrylate is preferable.

(Content of each component or structural unit in raw material monomer (a) or vinyl polymer)
The content in the raw material monomer (a) containing (a-1), (a-2) and (a-3) (the content as an unneutralized amount; the same shall apply hereinafter) during the production of the vinyl polymer, or The content of the structural unit derived from (a-1), the structural unit derived from (a-2), and the structural unit derived from (a-3) in the vinyl polymer determines the dispersion stability of the pigment-containing polymer particles. From the viewpoint of improving
The content of (a-1) is preferably 5% by mass or more, more preferably 10% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less, and still more preferably 20% by mass. It is below.
The content of (a-2) is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass. 75% by mass or less, more preferably 75% by mass or less.
When (a-3) is contained, its content is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less. .

The mass ratio [(a-1)/(a-2)] of (a-1) to (a-2) is preferably 0.1 or more, more preferably 0.2 or more, and preferably It is 1.2 or less, more preferably 1.0 or less, and still more preferably 0.8 or less.
In the present invention, the contents of structural units derived from (a-1), (a-2), and (a-3) in the vinyl-based polymer can be determined by measurement, and the vinyl-based resin polymer The charging ratio of raw material monomers (a) including (a-1), (a-2) and (a-3) at the time of production can be substituted. Of these, (a-1) is preferably determined by potentiometric titration, and (a-2) and (a-3) are preferably determined by using the charging ratio of the raw material monomer (a).

(Production of vinyl polymer)
The vinyl-based polymer is produced by copolymerizing the raw material monomer (a) by known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among these polymerization methods, the solution polymerization method is preferred.
Solvents used in the solution polymerization method are not particularly limited, but polar organic solvents are preferred. Examples of polar organic solvents include aliphatic alcohols having 1 to 3 carbon atoms, ketones having 3 to 5 carbon atoms, ethers, and esters such as ethyl acetate. Among these, ethanol, acetone, methyl ethyl ketone, or a mixed solvent of one or more of these and water are preferred, and methyl ethyl ketone or a mixed solvent of it and water are preferred.
A polymerization initiator and a polymerization chain transfer agent can be used in the polymerization.
Examples of polymerization initiators include azo compounds such as 2,2'-azobisisobutyronitrile and 2,2'-azobis(2,4-dimethylvaleronitrile), tert-butyl peroxyoctoate, benzoyl peroxide, and the like. A known polymerization initiator such as an organic peroxide of can be used. The amount of the radical polymerization initiator is preferably 0.001 mol or more and 5 mol or less, more preferably 0.01 mol or more and 2 mol or less per 1 mol of the raw material monomer (a).
Examples of polymerization chain transfer agents include carboxy group-containing mercaptans such as 2-mercaptopropionic acid; alkyl mercaptans such as octanethiol; hydroxy group-containing mercaptans such as 2-mercaptoethanol and 3-mercapto-1,2-propanediol. known polymerization chain transfer agents can be used.
Moreover, there is no restriction on the chain mode of the polymerization monomers, and any polymerization mode such as random, block, or graft may be used.

Preferred polymerization conditions vary depending on the type of polymerization initiator, monomer, solvent, etc. used, but usually the polymerization temperature is preferably 30° C. or higher, more preferably 50° C. or higher, and preferably 95° C. or lower. More preferably, it is 90° C. or less. The polymerization time is preferably 1 hour or more, more preferably 2 hours or more, and preferably 20 hours or less, more preferably 10 hours or less. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.
After completion of the polymerization reaction, the polymer produced can be isolated from the reaction solution by known methods such as reprecipitation and solvent distillation. The obtained polymer can be purified by removing unreacted monomers and the like by reprecipitation, membrane separation, chromatography, extraction, or the like.

In the present invention, the pigment-containing polymer particles preferably have a crosslinked structure partially or wholly. The crosslinked structure refers to a state in which some or all of the ionic groups of the polymer-type dispersant constituting the pigment-containing polymer particles have reacted with a compound having at least a plurality of functional groups capable of reacting with the ionic groups. means. Even if the polymer-type dispersant is a water-soluble polymer before being cross-linked with a cross-linking agent, it becomes a water-insoluble polymer by having a cross-linked structure.
When the pigment-containing polymer particles are crosslinked with a crosslinking agent, it is difficult to measure the molecular weight of the polymer-type dispersant that constitutes the pigment-containing polymer particles. The weight-average molecular weight of the polymer-type dispersant in the form of is preferably 2,000 or more, more preferably 5,000 or more, from the viewpoint of improving adsorption to pigments and dispersion stability, and preferably 20,000 or less, more preferably 18,000 or less.
The weight average molecular weight is measured by the method described in Examples.

[Production of polymer particles containing pigment]
Pigment-containing polymer particles can be efficiently produced as an aqueous pigment dispersion by a method comprising steps 1 and 2 below.
Moreover, from the viewpoint of improving the ejection stability of the ink obtained using the polymer particles containing the pigment, it is preferable to further perform the step 3 (crosslinking step).
Step 1: Process of dispersing a pigment mixture containing a pigment, a polymer a, an organic solvent, and water to obtain a dispersed product Step 2: Removing the organic solvent from the dispersed product obtained in Step 1 to contain the pigment Step 3: Add a cross-linking agent to the aqueous dispersion of the pigment-containing polymer particles obtained in Step 2 to cross-link some or all of the pigment-containing polymer particles. process

(Step 1)
Step 1 is a step of obtaining a dispersion treated product in which the pigment is finely divided by the polymer a in an aqueous medium containing an organic solvent. Here, the "polymer a" is a polymer dispersant that constitutes a pigment-containing polymer particle through a neutralization reaction and, if necessary, a cross-linking reaction, i.e., a precursor of the polymer dispersant in the present invention. means a polymer that is As the polymer a, a vinyl-based polymer obtained by copolymerizing raw material monomers (a) containing an ionic monomer (a-1) and a hydrophobic monomer (a-2) is preferable, and a nonionic monomer (a- A vinyl polymer obtained by copolymerizing 3) is more preferable. As a specific procedure of step 1, it is preferable to mix the polymer with an organic solvent, pigment, water, a neutralizing agent, and, if necessary, a surfactant and the like, and then apply necessary stress.
The organic solvent used in step 1 is not limited, but ketones, ethers, esters, aliphatic alcohols having 1 to 3 carbon atoms, etc. are preferable, and wettability to pigments, solubility of polymer a and pigments From the viewpoint of improving adsorptivity, ketones having 4 to 8 carbon atoms are more preferred, methyl ethyl ketone and methyl isobutyl ketone are more preferred, and methyl ethyl ketone is even more preferred. When a vinyl-based polymer is synthesized as the polymer a by a solution polymerization method, the solvent used in the polymerization may be used as it is.
The mass ratio of the organic solvent to the polymer a in the pigment mixture [organic solvent/polymer a] is preferably 0.4 or more, more preferably 0, from the viewpoint of wettability to the pigment, adsorptivity, and solubility of the polymer a. .6 or more, and preferably 2 or less, more preferably 1.5 or less.

When the polymer a has acid groups, at least part of the acid groups are preferably neutralized using a neutralizing agent. It is believed that this increases the charge repulsive force that develops after neutralization, suppresses aggregation of the pigment-containing polymer particles in the ink of the present invention, suppresses thickening, and improves storage stability.
When neutralizing, the neutralization is preferably carried out so that the pH of the ink of the present invention is 7 or more and 11 or less.
Examples of the neutralizing agent include bases such as lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia and various amines, preferably sodium hydroxide and ammonia.
Neutralizing agents can be used alone or in combination of two or more.
From the viewpoint of improving storage stability, the use equivalent of the neutralizing agent is preferably 10 mol% or more, more preferably 20 mol% or more, still more preferably 30 mol% or more, and preferably 150 mol% or less. , more preferably 120 mol % or less, still more preferably 100 mol % or less. Here, the use equivalent of the neutralizing agent can be determined by the following formula.
Equivalent weight of neutralizing agent used (% by mole)=[{adding mass of neutralizing agent (g)/equivalent weight of neutralizing agent}/[{acid value of polymer a (mgKOH/g)×mass of polymer a (g) }/(56×1,000)]]×100

In the dispersion treatment in step 1, the pigment can be atomized to a desired particle size only by the main dispersion by shear stress. Furthermore, it is preferable to carry out main dispersion.
As a dispersing machine used for pre-dispersion, generally used mixing and stirring devices such as anchor blades and disper blades can be used.
Means for imparting shear stress used for this dispersion include, for example, kneaders such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media type dispersers such as paint shakers and bead mills. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment.

(Step 2)
Step 2 is a step of removing the organic solvent from the dispersed product obtained in Step 1 to obtain an aqueous dispersion of polymer particles containing a pigment. Removal of the organic solvent can be performed by a known method. It is preferable that the organic solvent in the resulting aqueous dispersion of pigment-containing polymer particles is substantially removed, but it may remain as long as the object of the present invention is not impaired. The amount of residual organic solvent is preferably 0.1% by mass or less, more preferably 0.01% by mass or less.

(Step 3)
Step 3 is a step of adding a cross-linking agent to the aqueous dispersion of the pigment-containing polymer particles obtained in Step 2 to form a cross-linked structure.
In step 3, part or all of the ionic groups of the polymer a constituting the pigment-containing polymer particles are reacted with a cross-linking agent to form a cross-linked structure in part or all of the pigment-containing polymer particles. It is believed that this causes the polymer-type dispersant to be strongly adsorbed or immobilized on the surface of the pigment, suppressing aggregation of the pigment and, as a result, further improving the ejection stability of the resulting ink.

(crosslinking agent)
As the cross-linking agent for forming a cross-linked structure in the aqueous dispersion of the polymer particles containing the pigment, from the viewpoint of efficiently cross-linking with the ionic groups of the polymer a and improving the ejection stability of the ink of the present invention, includes compounds having 2 or more and 6 or less, preferably 4 or less epoxy groups.
The molecular weight of the cross-linking agent is preferably 120 or more, more preferably 180 or more, and preferably 2,000 or less, more preferably 1,000 or less, from the viewpoint of improving reaction easiness and storage stability. .
The epoxy equivalent of the cross-linking agent is preferably 90 or more, more preferably 100 or more, still more preferably 110 or more, and preferably 300 or less, more preferably 200 or less, still more preferably 150 or less.
The water content of the cross-linking agent is preferably 50 mass % or less, more preferably 40 mass % or less, from the viewpoint of efficiently cross-linking the polymer a in an aqueous medium. Here, the water solubility refers to the dissolution rate (% by mass) when 10 parts by mass of a cross-linking agent is dissolved in 90 parts by mass of water at room temperature of 25°C.
Specific examples of the cross-linking agent include those described in paragraph [0041] of JP-A-2018-80255. Among them, water-insoluble compounds are preferred, polyglycidyl ether compounds of polyhydric alcohols having a hydrocarbon group of 3 to 8 carbon atoms are more preferred, and selected from pentaerythritol polyglycidyl ether and trimethylolpropane polyglycidyl ether. more preferably one or more.

From the viewpoint of improving ejection stability, the cross-linking ratio in step 3 is the ratio of the number of molar equivalents of the cross-linkable functional group of the cross-linking agent to the number of molar equivalents of the ionic group of the polymer a, and is preferably 10 mol % or more, or more. Preferably 20 mol% or more, more preferably 30 mol% or more, still more preferably 40 mol% or more, and preferably 80 mol% or less, more preferably 70 mol% or less, still more preferably 60 mol% or less is.
The temperature of the cross-linking treatment is preferably 40° C. or higher, more preferably 50° C. or higher, still more preferably 60° C. or higher, and preferably 95° C. or lower, more preferably 85° C. or lower, from the same viewpoint as described above. , and more preferably 75°C or less.
The time for the cross-linking treatment is preferably 0.5 hours or more, more preferably 1 hour or more, and preferably 12 hours or less, more preferably 8 hours or less, and further from the viewpoint of completion of the cross-linking reaction and economy. It is preferably 5 hours or less.

The solid content concentration of the aqueous dispersion of the pigment-containing polymer particles is preferably 10 from the viewpoint of improving the dispersion stability of the aqueous dispersion of the pigment-containing polymer particles and from the viewpoint of facilitating the production of the ink of the present invention. % by mass or more, more preferably 15% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less. The solid content concentration is measured by the method described in Examples.
The content of the pigment in the aqueous dispersion of the pigment-containing polymer particles is preferably 5% by mass or more, more preferably 5% by mass or more, from the viewpoint of the dispersion stability of the aqueous dispersion of the pigment-containing polymer particles and the ink of the present invention. It is 7% by mass or more, more preferably 10% by mass or more, and preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less.
The mass ratio [pigment/polymer a] of the pigment to the polymer a in the aqueous dispersion of the polymer particles containing the pigment is preferably 50/50 or more, more preferably 55/45 or more, and still more preferably 60/40 or more. Yes, and preferably 90/10 or less, more preferably 85/15 or less, and even more preferably 80/20 or less.
The weight ratio of the pigment to the polymeric dispersant [pigment/polymeric dispersant] in the aqueous dispersion of the pigment-containing polymer particles is preferably 51/49 or more, more preferably 56/44 or more, and still more preferably 61. /39 or more, and preferably 91/9 or less, more preferably 86/14 or less, and even more preferably 81/21 or less.

The average particle diameter of the aqueous dispersion of the pigment-containing polymer particles is preferably 40 nm or more, more preferably 50 nm or more, from the viewpoint of improving the storage stability of the aqueous dispersion of the pigment-containing polymer particles and the ink of the present invention. , more preferably 60 nm or more, still more preferably 70 nm or more, still more preferably 80 nm or more, and preferably 200 nm or less, more preferably 170 nm or less, even more preferably 150 nm or less, still more preferably 140 nm or less, and more More preferably, it is 120 nm or less.
The average particle size is measured by the method described in Examples.

<Polymer Particles Not Containing Pigment>
From the viewpoint of improving the tackiness of the resulting printed material, the ink of the present invention preferably further contains polymer particles containing no pigment as a fixing aid polymer. Preferably, the pigment-free polymer particles are capable of forming a dispersion in an aqueous medium.
The polymer constituting the pigment-free polymer particles (hereinafter also referred to as "polymer b") may be either a water-soluble polymer or a water-insoluble polymer, but is more preferably a water-insoluble polymer.
The definition of "water-insoluble polymer" is as described above.
The polymer b and the polymer a may have different compositions, or may be the same polymer including the composition, and may differ only in the presence or absence of a pigment.
When the ink contains pigment-containing polymer particles and pigment-free polymer particles, the polymer content in the ink is the total amount of polymer a and polymer b.
The pigment-free polymer particles may be crosslinked with a crosslinking agent.

Polymer b is preferably one or more selected from acrylic resins, polyester resins, and polyurethane resins. Among them, polymer b is preferably an acrylic resin containing a structural unit derived from (meth)acrylic acid (b-1) and a structural unit derived from (meth)acrylic acid ester (b-2).
(Meth)acrylic acid (Sb-1) is preferably at least one selected from acrylic acid and methacrylic acid, more preferably methacrylic acid, from the viewpoint of improving the tackiness of the resulting printed material.
(Meth)acrylic acid ester (b-2), from the same viewpoint as above, methyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, At least one selected from 2-ethylhexyl (meth)acrylate and cyclohexyl (meth)acrylate is preferable, and methyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and ( At least one selected from cyclohexyl meth)acrylate is more preferred, and 2-ethylhexyl (meth)acrylate is even more preferred.
The polymer b may contain structural units derived from monomers other than (meth)acrylic acid (b-1) and acrylic acid ester (b-2). Other monomers include ionic monomers other than (meth)acrylic acid, hydrophobic monomers having an aromatic group, or nonionic monomers, among which the hydrophobic monomer (b-3) having an aromatic group is preferred. . Examples of such hydrophobic monomers (b-3) include the aforementioned styrene-based monomers, aromatic group-containing (meth)acrylates, aromatic group-containing macromonomers, and the like.

The content of the structural unit derived from each component in the polymer b is as follows from the viewpoint of improving the tackiness of the resulting printed material.
The content of structural units derived from (meth)acrylic acid (b-1) in polymer b is preferably 1% by mass or more, more preferably 1.5% by mass or more, and still more preferably 2% by mass or more, The content is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.
The content of structural units derived from (meth)acrylic acid ester (b-2) in polymer b is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more, and , preferably 99% by mass or less, more preferably 98.5% by mass or less, and still more preferably 98% by mass or less.
Mass ratio of (meth) acrylic acid (b-1) and (meth) acrylic ester (b-2) [(meth) acrylic acid (b-1)/(meth) acrylic ester (b-2)] is preferably 0.01 or more, more preferably 0.02 or more, and preferably 0.5 or less, more preferably 0.2 or less, still more preferably 0.1 or less.

The weight-average molecular weight of the polymer b is preferably 50,000 or more, more preferably 100,000 or more, and still more preferably 200,000 or more, from the viewpoint of improving the storage stability of the ink of the present invention and improving the tackiness of printed matter. , and preferably 2,000,000 or less, more preferably 1,500,000 or less, and still more preferably 1,000,000 or less. The weight average molecular weight is measured by the method described in Examples.
From the same viewpoint as above, the average particle diameter of the pigment-free polymer particles is preferably 20 nm or more, more preferably 40 nm or more, still more preferably 60 nm or more, and preferably 150 nm or less, more preferably 130 nm or less. , and more preferably 110 nm or less. The average particle size is measured by the method described in Examples.

[Production of Pigment-Free Polymer Particles]
The pigment-free polymer particles may be appropriately synthesized or commercially available, but those that can form an aqueous dispersion are preferred. When an aqueous dispersion of pigment-free polymer particles is obtained, the polymer b constituting the pigment-free polymer particles is preferably neutralized with a neutralizing agent.
An aqueous dispersion of pigment-free polymer particles is obtained by obtaining polymer b' before neutralization of polymer b constituting the pigment-free polymer particles by a known polymerization method, followed by adding the polymer b', water, and necessary Depending on the method, the mixture containing the neutralizing agent is stirred while being heated, and then the temperature is lowered.

The preferred structural units, content, physical properties and the like of the polymer b' before neutralization are the same as those of the polymer b, and it is preferably obtained by the same polymerization method as the vinyl resin.
The acid value of polymer b′ is preferably 0 mgKOH/g or more, more preferably 5 mgKOH/g or more, more preferably 10 mgKOH/g or more, still more preferably 15 mgKOH/g or more, and preferably 200 mgKOH/g or less, It is more preferably 100 mgKOH/g or less, still more preferably 50 mgKOH/g or less, still more preferably 20 mgKOH/g or less.
The temperature at which the mixture is stirred is preferably 60° C. or higher, more preferably 70° C. or higher, still more preferably 75° C. or higher, and preferably 100° C. or lower, more preferably 95° C. or lower. The stirring time is preferably 0.5 hours or longer, more preferably 0.8 hours or longer, and preferably 10 hours or shorter, more preferably 5 hours or shorter.

The neutralizing agent used in the production of the aqueous dispersion of polymer particles containing no pigment is preferably alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, ammonia, organic amines, and the like, and more preferably hydroxides. Sodium, triethanolamine.
The use equivalent of the neutralizing agent is 0 mol % or more, preferably 10 mol % or more, more preferably 30 mol % or more, and preferably 160 mol %, from the viewpoint of the dispersion stability of the pigment-free polymer particles. % or less, more preferably 130 mol % or less, still more preferably 110 mol % or less. The use equivalent of the neutralizing agent can be determined by the method described above.

[Production of the ink of the present invention]
The ink of the present invention comprises an aqueous dispersion of polymer particles containing a pigment, a water-soluble organic solvent to be described later, an aqueous dispersion of polymer particles containing no pigment as needed, a silicone surfactant, and other components. can be efficiently produced by mixing the organic solvent and other surfactants. There is no particular limitation on the method of mixing them.

<Water-soluble organic solvent>
The water-soluble organic solvent used in the present invention may be liquid or solid at 25°C. be.
The water-soluble organic solvent contains propylene glycol (S1) and glycol ether (S2) from the viewpoint of achieving both an improvement in ejection stability and an improvement in tackiness.
In the present invention, propylene glycol (S1) mainly suppresses the evaporation of water from the ink nozzles, and quickly volatilizes after printing, thereby forming a strong ink film with a minimum drying process. Glycol ether (S2) is thought to have a function of suppressing adhesion to the back surface, and mainly plays a role in maintaining an appropriate liquid surface shape in the ink nozzle. By using them in specific ranges, it is considered possible to achieve both an improvement in ejection stability and an improvement in tackiness.

Glycol ethers (S2) include ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monopropyl ether, Diethylene glycol monoisobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoisobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl One or more selected from ether (boiling point 241° C.), tripropylene glycol monobutyl ether and the like can be mentioned.
Among these, at least one selected from diethylene glycol monoisobutyl ether and diethylene glycol monobutyl ether is preferable from the viewpoint of appropriately maintaining the spread of the ink on the low-absorption print medium.

The ink of the present invention may contain propylene glycol (S1), polyhydric alcohols other than glycol ether (S2), amide compounds, and the like, if necessary.
Polyhydric alcohols include ethylene glycol, 1,2-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, dipropylene glycol, 1,2 -octanediol, 1,8-octanediol, 1,2-decanediol, 1,3-propanediol, 2-ethyl-1,3-hexanediol, diethylene glycol, 1,2,6-hexanetriol, 1,2 ,4-butanetriol, 1,2,3-butanetriol, petriol and the like.
Amide compounds include 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-butyl-2-pyrrolidone, 5-methyl-2-pyrrolidone and the like. mentioned.

<Surfactant>
The ink of the present invention contains a surfactant from the viewpoint of improving the wettability to the print medium.
As the surfactant, at least a silicone-based surfactant is contained. Further, from the viewpoint of maintaining proper surface tension of the ink and improving wettability to the printing medium, other nonionic surfactants are preferable, and it is more preferable to use acetylene glycol-based surfactants together.

(Silicone-based surfactant)
Examples of silicone-based surfactants include dimethylpolysiloxane, polyether-modified silicone, amino-modified silicone, carboxy-modified silicone, and the like. From the same viewpoint as above, polyether-modified silicone is preferred.
Polyether-modified silicone-based surfactants have a structure in which side chains and/or terminal hydrocarbon groups of silicone oil are substituted with polyether groups. The polyether group is preferably a polyethyleneoxy group, a polypropyleneoxy group, or a polyalkyleneoxy group in which an ethyleneoxy group (EO) and a propyleneoxy group (PO) are added blockwise or randomly. A compound in which an ether group is grafted, a compound in which a silicone and a polyether group are bonded in blocks, and the like can be used.

The HLB (hydrophilic-lipophilic balance) value of the polyether-modified silicone surfactant is preferably 2 or more, more preferably 3 or more, still more preferably 4 or more, and most preferably 7, from the viewpoint of solubility in ink. That's it. In addition, from the viewpoint of appropriately controlling wetting and spreading on a medium with low liquid absorption, it is preferably 14 or less, more preferably 13 or less, and most preferably 12 or less. Here, the HLB value can be determined by the Griffin method.
In addition, the kinematic viscosity at 25° C. of the polyether-modified silicone surfactant is preferably 50 mm ² /s or more, more preferably 80 mm ² /s or more, and preferably 500 mm ² /s or less, more preferably 300 mm ² /s or less. The kinematic viscosity can be obtained with an Ubbelohde viscometer.
Specific examples of polyether-modified silicone surfactants include KF series manufactured by Shin-Etsu Chemical Co., Ltd.; KF-353 (HLB10), KF-355A (HLB12), KF-642 (HLB12), etc., Silface SAG005 (HLB7) manufactured by Co., Ltd., FZ-2191 (HLB5) manufactured by NUC Co., Ltd., BYK-333 (HLB10) manufactured by BYK-Chemie Japan Co., Ltd., and the like.

(Acetylene glycol surfactant)
Examples of acetylene glycol surfactants include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3, 5-dimethyl-1-hexyne-3-ol, 2,4-dimethyl-5-hexyne-3-ol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,5,8,11- acetylenic diols such as tetramethyl-6-dodecyne-5,8-diol, and their ethylene oxide adducts;
The average addition mole number sum (n) of the ethyleneoxy group (EO) of the ethylene oxide adduct is preferably 1 or more, more preferably 1.5 or more, and preferably 20 or less, more preferably 10 or less. is.
Examples of commercially available acetylene glycol-based surfactants include "Surfinol" series and "Olfine" series manufactured by Nissin Chemical Industry Co., Ltd., and "Acetylenol" series manufactured by Kawaken Fine Chemicals Co., Ltd., and the like. Among these, Surfynol 420 (n: 1.3), Surfynol 440 (n: 3.5), Surfynol 465 (n: 10.0), Surfynol 485 (n: 30.0), Olphine E1010 , acetylenol E100, acetylenol E200, acetylenol E40 (n:4), acetylenol E60 (n:6), acetylenol E81 (n:8), acetylenol E100 (n:10), and the like.
The ink of the present invention may further contain various additives such as viscosity modifiers, antifoaming agents, preservatives, antifungal agents, and antirust agents that are commonly used in inks.

The content of each component of the ink of the present invention and the physical properties of the ink are as follows.
(Pigment content)
The content of the pigment in the ink of the present invention is preferably 1% by mass or more, more preferably 3% by mass or more, and still more preferably 4% by mass or more, from the viewpoint of improving print density. is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 7% by mass or less.
(Content of polymer particles containing pigment)
The content of the pigment-containing polymer particles in the ink of the present invention is preferably 3% by mass or more, more preferably 4% by mass or more, and still more preferably 5% by mass or more, from the viewpoint of improving print density. , from the viewpoint of improving storage stability, it is preferably 15% by mass or less, more preferably 13% by mass or less, and still more preferably 10% by mass or less.

(Content of polymer particles not containing pigment)
The content of the pigment-free polymer particles in the ink of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, and still more preferably 2% by mass, from the viewpoint of improving the tackiness of the resulting printed material. % or more, and preferably 8% by mass or less, more preferably 7% by mass or less, and even more preferably 6% by mass or less.
The total amount of polymer a and polymer b in the ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, and still more preferably 3% by mass or more, from the viewpoint of improving the tackiness of the resulting printed matter. and preferably 10% by mass or less, more preferably 9% by mass or less, and even more preferably 8% by mass or less.

(Content of water-soluble organic solvent)
The content of the water-soluble organic solvent in the ink of the present invention is preferably 4% by mass or more, more preferably 5% by mass or more, and still more preferably 8% by mass or more, from the viewpoint of improving the tackiness of the resulting printed matter. and is 30% by mass or less, preferably 28% by mass or less, more preferably 25% by mass or less.
The content of propylene glycol (S1) in the ink is less than 20% by mass, preferably 19% by mass or less, more preferably 17% by mass or less, and even more preferably, from the viewpoint of improving the tackiness of the resulting printed matter. It is 15% by mass or less, preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 6% by mass or more, and even more preferably 8% by mass or more.
The total content of propylene glycol (S1) and glycol ether (S2) in the ink is 4% by mass or more, preferably 5% by mass or more, and more preferably 8% by mass or more, from the viewpoint of improving ejection stability. and is 25% by mass or less, preferably 24% by mass or less, more preferably 23% by mass or less, and still more preferably 22% by mass or less.
The mass ratio [(S2)/(S1)] of the glycol ether (S2) to the propylene glycol (S1) is 0.1 or more, preferably 0.2 or more, more preferably 0.2 or more, from the viewpoint of improving ejection stability. is greater than or equal to 0.3 and less than or equal to 0.6, preferably less than or equal to 0.5.

(Content of surfactant)
From the viewpoint of improving ejection stability, the content of the surfactant in the ink of the present invention is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.5% by mass or more. and is preferably 5% by mass or less, more preferably 4% by mass or less, and still more preferably 3% by mass or less.
From the same viewpoint as above, the content of the silicone-based surfactant in the ink of the present invention is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and still more preferably 0.05% by mass or more. and is preferably 3% by mass or less, more preferably 2% by mass or less, and still more preferably 1% by mass or less.
From the same viewpoint as above, the content of the acetylene glycol-based surfactant in the ink of the present invention is preferably 0.2% by mass or more, more preferably 0.4% by mass or more, and still more preferably 0.6% by mass. and preferably 4% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less.

The ratio of the acetylene glycol-based surfactant to the silicone-based surfactant in the ink of the present invention (acetylene glycol-based surfactant/silicone-based surfactant) is preferably 1% by mass or more from the same viewpoint as above. It is preferably 2% by mass or more, more preferably 3% by mass or more, and preferably 10% by mass or less, more preferably 8% by mass or less, and more preferably 6% by mass or less.
(water content)
The content of water in the ink of the present invention is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass. % or less, more preferably 85 mass % or less.

(Mass ratio of polymer particles containing pigment/water-soluble organic solvent)
The mass ratio of the pigment-containing polymer particles to the water-soluble organic solvent (pigment-containing polymer particles/water-soluble organic solvent) is preferably 0.1 or more, more preferably 0.1 or more, from the viewpoint of improving the tackiness of the resulting printed material. is 0.2 or more, more preferably 0.25 or more, and is preferably 1.5 or less, more preferably 1.2 or less, and still more preferably 0.8 or less.

(Physical properties of the ink of the present invention)
The viscosity of the ink of the present invention at 32° C. is preferably 2 mPa·s or more, more preferably 2.5 mPa·s or more, still more preferably 3 mPa·s or more, from the viewpoint of achieving both ejection stability and tackiness, and , preferably less than 5 mPa·s, more preferably 4.5 mPa·s or less, still more preferably 4 mPa·s or less.
Ink viscosity is measured by the method described in Examples.
The pH of the ink of the present invention is preferably 7.0 or higher, more preferably 7.2 or higher, and still more preferably 7.5 or higher, from the viewpoint of storage stability, material resistance, and skin irritation. It is 11 or less, more preferably 10 or less, and still more preferably 9.5 or less.
The ink of the present invention is particularly suitable as a water-based inkjet ink for flexible packaging printing and label/seal printing. In addition, flexible packaging printing and label/sticker printing mean printing on a thin and flexible material such as a resin film alone or on a laminated material. Printed matter printed on flexible packaging using the ink of the present invention is suitable for use in packaging foods, daily necessities, and the like.
The ink of the present invention is preferably used as a set by combining a plurality of inks having different colors, and is suitable for full-color printing.

[Inkjet printing method]
The inkjet printing method of the present invention is a method of printing on a low-absorption printing medium using the ink of the present invention. An image or the like is printed by ejecting droplets.

(Low Absorbent Print Media)
Examples of low liquid-absorption print media include print media made of metal, synthetic resin, low-absorption coated paper, art paper, and the like.
Examples of metals include iron and iron alloys, aluminum and aluminum alloys, and aluminum and aluminum alloys are more preferable. Also preferred are metal foils and metal plates subjected to various surface treatments, and laminates in which metal is coated with a resin film such as polyester or polyolefin.
Synthetic resins include polyvinyl chloride, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, polypropylene, polystyrene, polyamide, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-styrene copolymer, polycarbonate, PC and ABS (50/ 50) Polymer alloys, triacetyl cellulose and the like. In addition, those subjected to corona discharge treatment and those subjected to biaxial stretching are also preferable. Among these, polyester resins such as polyvinyl chloride and polyethylene terephthalate, and polypropylene are preferred. Polypropylene is most preferred.

In inkjet printing, from the viewpoint of improving the tackiness of the resulting printed matter, it is preferable to heat the surface temperature of the printing medium to 30° C. or higher and 100° C. or lower depending on the material.
The surface temperature of the print medium is preferably 35° C. or higher, more preferably 40° C. or higher in the case of a resin film, and preferably 80° C. or lower, more preferably 75° C. or lower in the case of a metal foil. , preferably 50° C. or higher, more preferably 60° C. or higher, and preferably 95° C. or lower, more preferably 90° C. or lower.
Examples of the method for heating the print medium include known methods such as a method of irradiating infrared rays, a method of exposing to a heated atmosphere in an oven or the like, and a method of contacting with a heated object such as metal.

In the following Production Examples, Preparation Examples, Examples and Comparative Examples, "parts" and "%" are "mass parts" and "mass%" unless otherwise specified. In addition, the measuring method of each physical property etc. is as follows.

(1) Measurement of weight-average molecular weights of polymer a and polymer b Using a solution obtained by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol/L and 50 mmol/L, respectively, as an eluent, Gel permeation chromatography [Tosoh Corporation GPC device (HLC-8320GPC), Tosoh Corporation columns (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolum Super AW-H), flow rate: 0.5 mL / min], Monodisperse polystyrene kits with known molecular weights [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500) manufactured by Tosoh Corporation].
A sample to be measured was obtained by mixing 0.1 g of polymer with 10 mL of the eluent in a glass vial, stirring with a magnetic stirrer at 25° C. for 10 hours, and using a syringe filter (manufactured by Advantech, DISMIC-13HP PTFE 0.2 μm). and used after filtration.

(2) Measurement of average particle size of polymer particles containing pigment and polymer particles not containing pigment Cumulant analysis is performed using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.) to determine the average particle size. It was measured. A dispersion diluted with water was used so that the concentration of particles to be measured was 5×10 ⁻³ wt % (converted to solid concentration). The measurement conditions are a temperature of 25 ° C., an angle between the incident light and the detector of 90 °, and the number of times of accumulation of 100 times. The particle size was defined as the average particle size of the pigment-containing polymer particles and the pigment-free polymer particles.

(3) Measurement of solid content concentration Using an infrared moisture meter "FD-230" (manufactured by Ketsuto Kagaku Kenkyusho Co., Ltd.), 5 g of the measurement sample is dried at 150 ° C., measurement mode 96 (monitoring time 2.5 minutes / fluctuation After drying under the condition of width 0.05%), the water content (%) of the measurement sample was measured, and the solid content concentration was calculated by the following formula.
Solid content concentration (%) = 100 - moisture of measurement sample (%)

(4) Measurement of water solubility of epoxy compound 90 parts by mass of ion-exchanged water and 10 parts by mass of epoxy compound (W1) were added to a glass tube (25 mmφ x 250 mmh) at room temperature of 25°C, and the glass tube was heated to a water temperature of 25°C. It was left still for 1 hour in the adjusted constant temperature bath. Then, the glass tube was vigorously shaken for 1 minute and then allowed to stand again in the constant temperature bath for 12 hours. Then, the undissolved matter that separated from water and precipitated or floated was recovered, dried for 6 hours under an environment of 40° C. and a gauge pressure of −0.08 MPa, and then weighed (W2). The water content (% by mass) was calculated by the following formula.
Water solubility (mass%) = {(W1-W2)/W1} x 100

(5) Viscosity of ink Using an E-type viscometer “TV-25” (manufactured by Toki Sangyo Co., Ltd., standard cone rotor 1°34′×R24, rotation speed 50 rpm), the viscosity was measured at 32 ° C. .

Production Example 1 (Production of water-insoluble polymer a solution)
In a reaction vessel, 10 parts of methyl ethyl ketone (MEK), 0.02 parts of a polymerization chain transfer agent (2-mercaptoethanol), and 20% each of each monomer shown in Table 1 are added and mixed, and the nitrogen gas is sufficiently replaced. to obtain a mixed solution.
On the other hand, the remaining 80% of each monomer shown in Table 1 was charged into a dropping funnel, then 0.08 part of the polymerization chain transfer agent, 80 parts of MEK and a polymerization initiator [2,2'-azobis(2, 4-dimethylvaleronitrile)] was added and mixed, and the mixture was sufficiently replaced with nitrogen gas to obtain a mixed solution.
Under a nitrogen atmosphere, the mixed solution in the reaction vessel was heated to 75° C. while stirring, and the mixed solution in the dropping funnel was gradually dropped into the reaction vessel over 3 hours. After the completion of dropping, the liquid temperature of the mixed solution was maintained at 75°C for 2 hours, a solution obtained by dissolving 0.6 parts of the polymerization initiator in 10 parts of MEK was added to the mixed solution, and the mixture was further heated at 75°C for 1 hour. After repeating three times, aging was carried out at 85° C. for 2 hours to obtain a polymer solution.
A portion of the resulting polymer solution was dried at 105° C. under reduced pressure for 2 hours to remove the solvent to isolate the water-insoluble polymer a. The weight average molecular weight of the obtained water-insoluble polymer a was 60,000.

The details of the monomers shown in Table 1 are as follows.
- (a-2) Styrene macromer: manufactured by Toagosei Co., Ltd., trade name: AS-6S, number average molecular weight: 6000, polymerizable functional group: methacryloyloxy group - (a-3) polypropylene glycol monomethacrylate (propylene oxide Average number of moles added: 9): NOF Co., Ltd., trade name: Blemmer PP-500

Preparation Example 1 (Preparation of aqueous dispersion (crosslinked) of polymer particles containing pigment)
(1) 58.1 parts of polymer a obtained by drying the MEK solution of water-insoluble polymer a obtained in Production Example 1 under reduced pressure was mixed with 71.5 parts of MEK, and further a 5N sodium hydroxide aqueous solution (NaOH solid content 16.9%, Fuji Film Wako Pure Chemical Co., Ltd.) 9.9 parts were added and neutralized so that the ratio of the number of moles of NaOH to the number of moles of carboxy groups in the polymer was 40 mol% (degree of neutralization : 40 mol %). Furthermore, 695.1 parts of ion-exchanged water is added, 200 g of pigment (CI Pigment Black 7, Cabot Corporation "MONARCH 717") is added, and Disper (manufactured by Asada Iron Works Co., Ltd., Ultra Disper: trade name ) for 60 minutes at 20° C. with a disper blade rotating at 7000 rpm.
The resulting mixture was subjected to 9-pass dispersion treatment at a pressure of 150 MPa with a microfluidizer (manufactured by Microfluidics, trade name).

(2) Put 1000 g of the dispersed product obtained in (1) above into a 2 L eggplant flask, add 666.7 g of ion-exchanged water (solid content concentration: 15.0%), and use a rotary distillation apparatus "rotary evaporator N- 1000S" (manufactured by Tokyo Rika Kikai Co., Ltd.) at a rotation speed of 50 rpm in a hot bath adjusted to 32° C. and held at a pressure of 0.09 MPa for 3 hours to remove the organic solvent. Further, the hot bath was adjusted to 62° C., the pressure was lowered to 0.07 MPa, and the mixture was concentrated to a solid concentration of 25.0%.
(3) The obtained concentrate is put into a 500 ml angle rotor, and centrifuged at 7000 rpm for 20 minutes using a high-speed refrigerated centrifuge "himac CR22G" (manufactured by Hitachi Koki Co., Ltd., set temperature: 20 ° C.), The liquid layer portion was filtered through a 5 μm membrane filter “Minisart” (manufactured by Sartorius).
61.61 g of ion-exchanged water was added to 400 g of the filtrate (solid content: 77 g of C.I. Pigment Black 7, 22 g of the water-insoluble polymer a), and Proxel LVS (manufactured by Arch Chemicals Japan Co., Ltd.: antifungal agent , Effective content 20%) 1 g is added, and a crosslinking agent (Nagase ChemteX Corporation, Denacol EX-321L: trade name, trimethylolpropane polyglycidyl ether, epoxy equivalent 129, water solubility: 27%) 2.1 g. was added (crosslinking ratio: 40 mol%) and stirred at 70°C for 3 hours. After cooling to 25° C., the mixture was filtered through the 5 μm filter, and ion-exchanged water was added so that the solid content concentration was 18% to obtain an aqueous dispersion (crosslinked) of polymer particles containing pigment. The average particle size of the pigment-containing polymer particles in the resulting aqueous dispersion was 90 nm.

Preparation Example 2 (Preparation of aqueous dispersion (non-crosslinked) of polymer particles containing pigment)
Preparation Example 1 (3) was carried out in the same manner as in Preparation Example 1, except that no crosslinking agent was used, to obtain an aqueous dispersion (non-crosslinked) of polymer particles containing a pigment. The average particle size of the pigment-containing polymer particles in the resulting aqueous dispersion was 90 nm.

Production Example 2 (Production of aqueous dispersion of polymer particles containing no pigment)
In a reaction vessel equipped with a dropping funnel, the monomers shown in Table 2, "Initial charge monomer solution", Latemul E-118B (sodium polyoxyethylene alkyl ether sulfate, manufactured by Kao Corporation, surfactant), and a polymerization initiator. Potassium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and ion-exchanged water were added and mixed, followed by nitrogen gas replacement to obtain an initially charged monomer solution. Further, the monomer, surfactant, polymerization initiator, and deionized water shown in "Dripping monomer solution" in Table 2 were mixed to obtain a dropping monomer solution, which was placed in a dropping funnel and replaced with nitrogen gas.
Under a nitrogen atmosphere, the initially charged monomer solution in the reaction vessel was heated from room temperature to 80°C over 30 minutes while stirring. dripped inside. After the dropwise addition was completed, the mixture was stirred for 1 hour while maintaining the temperature in the reaction vessel. Then, the mixture was filtered through 200 mesh to obtain an aqueous dispersion of polymer particles containing no pigment (solid concentration: 44.1%, average particle size: 94 nm).
The water-insoluble polymer b constituting the pigment-free polymer particles had a weight average molecular weight of 750,000 and an acid value of 16 mgKOH/g.

Example 1 (Production of water-based ink)
Aqueous dispersion (crosslinked) of polymer particles containing pigment obtained in Preparation Example 1 (solid concentration: 18%, pigment: 13.6%, polymer: 4.4%) 33.0 g, 11.3 g of an aqueous dispersion of the obtained polymer particles containing no pigment (solid concentration: 44.1%), 11.5 g of propylene glycol (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.), diethylene glycol monoisobutyl ether (Fuji Film Wako Pure Chemical Industries, Ltd.) 3.5 g, silicone surfactant (manufactured by Nisshin Chemical Co., Ltd., polyether-modified silicone surfactant, Silface SAG005, wetting agent, HLB: 7, dynamic viscosity: 170 mm ² /s (25° C.)) 0.2 g, acetylene glycol-based surfactant (manufactured by Nissin Chemical Industry Co., Ltd., Surfynol 440; ethylene oxide (40%) adduct of Surfynol 104, average number of moles of ethylene oxide added: 3. 5) 1.0 g of ion-exchanged water was added so that the total amount was 100 g.

Examples 2 , 4 to 7, 10, 11, 13, 15, 16, Reference Examples 3, 8, 9, 12, 14, Comparative Examples 1 to 8 (production of water-based ink)
A water-based ink was obtained in the same manner as in Example 1, except that the compositions in Example 1 were changed to those shown in Tables 3 and 4.
In addition, Example 7 was carried out in the same manner as in Example 1 except that the aqueous dispersion (preparation of non-crosslinked) of the polymer particles containing the pigment obtained in Preparation Example 2 was used, and Reference Example 8 was prepared Same as Example 1 except that a self-dispersing carbon black pigment ("Cab-O-jet300" manufactured by Cabot Corporation) was used instead of the aqueous dispersion (crosslinked) of polymer particles containing the pigment obtained in Example 1. went to
The amounts of water dispersion, organic solvent, and surfactant in Tables 3 and 4 indicate the content (%) in the ink, and the water dispersion of polymer particles containing pigment and the amount of polymer particles not containing pigment. The amounts of water dispersion and self-dispersed carbon black pigment are solids amounts.
The silicone surfactant KF-355A is a polyether-modified silicone oil manufactured by Shin-Etsu Chemical Co., Ltd., and has an HLB of 12 and a kinematic viscosity of 150 mm ² /s (25° C.).

Using the obtained ink, a printed matter obtained by the following printing method was evaluated for ejection stability and tackiness by the following method. Table 3 shows the results.

<Inkjet printing method>
In an environment with a temperature of 25 ± 1 ° C and a relative humidity of 30 ± 5%, fill the cartridge of the print evaluation device (manufactured by Seiko Epson Corporation, inkjet printer, PX105, piezo type) with ink, and print A4 size at the print medium ejection part. A film heater (manufactured by Kawai Electric Co., Ltd.) is fixed so that the following print media can be heated, and corona discharge-treated polyethylene terephthalate film (manufactured by Futamura Chemical Co., Ltd.) is cut into A4 size and placed in the paper storage area. set.

<Discharge stability evaluation>
Using the printing evaluation apparatus, 10 sheets of solid images of 20 mm×20 mm were printed with 100% ink duty, and then left without printing for 30 minutes. After 30 minutes, the ejection stability was evaluated by calculating the ejection recovery rate (%) according to the following formula from the state of the solid printed matter obtained by printing one sheet of 20 mm×20 mm solid image. In this evaluation, the film heater was not energized.
Ejection recovery rate (%)=[(Ejection area of solid printed matter obtained by command to print 1 sheet)/(Ejection area of 10th solid printed matter obtained by command to print 10 sheets)]×100
(Evaluation criteria)
5: The ejection recovery rate is 90% or more.
4: The ejection recovery rate is 80% or more and less than 90%.
3: The ejection recovery rate is 70% or more and less than 80%.
2: The ejection recovery rate is 60% or more and less than 70%.
1: The ejection recovery rate is less than 60%.
If the evaluation is 3 or more, there is no practical problem, and if the evaluation is 4 or more, the practicality is excellent.

<Evaluation of tackiness>
The heating temperature of the film heater was set to 60°C.
Using the printing evaluation apparatus, one solid image of 20 mm×20 mm was printed with 100% ink duty. After that, the film was held for 1 hour at the print medium ejection portion to obtain a print for performance evaluation.
The same polyethylene terephthalate film as that used for printing was placed on the solid image portion of the obtained printed matter, and a cubic brass weight of 30 mm × 30 mm × 30 mm was placed thereon. After standing for 10 minutes in a constant humidity chamber, the state of transfer to a polyethylene terephthalate film placed on the solid image portion was observed, and tackiness (stickiness) was evaluated according to the following criteria.
(Evaluation criteria)
5: No stickiness (tack) and no image transfer.
4: Slightly sticky, but image transfer area is less than 2%.
3: Slightly sticky, but the transfer area of the image is 2% or more and less than 5%.
2: There is stickiness, and the transfer area of the image is 5% or more and less than 10%.
1: There is stickiness, and the transfer area of the image is 10% or more.
If the evaluation is 3 or more, there is no practical problem, and if the evaluation is 4 or more, the practicality is excellent.

From Tables 3 and 4, it can be seen that the inks of Examples can achieve both ejection stability and tackiness compared to the inks of Reference Examples and Comparative Examples.

Claims (8)

A water-based ink for inkjet printing on a low-absorption print medium,
Contains a pigment, a water-soluble organic solvent, and a silicone surfactant,
The water-soluble organic solvent contains propylene glycol (S1) and glycol ether (S2),
The content of propylene glycol (S1) in the ink is less than 20% by mass,
the total content of the propylene glycol (S1) and the glycol ether (S2) in the ink is 4% by mass or more and 23 % by mass or less;
mass ratio [(S2)/(S1)] of the glycol ether (S2) to the propylene glycol (S1) is 0.3 or more and 0.6 or less;
Viscosity at 32 ° C. is 2 mPa s or more and less than 4.5 mPa s ,
the pigment is in the form of pigment-containing polymer particles ;
Water-based ink for inkjet printing. The water-based ink for inkjet printing according to claim 1, wherein the glycol ether (S2) is one or more selected from diethylene glycol monobutyl ether and diethylene glycol monoisobutyl ether. The water-based ink for inkjet printing according to claim 1 or 2, wherein the viscosity at 32°C is 2 mPa·s or more and 4 mPa·s or less. 4. The water-based ink for inkjet printing according to any one of claims 1 to 3 , wherein the low-absorption print medium is a synthetic resin. The water-based ink for inkjet printing according to claim 4 , wherein the synthetic resin is polyethylene terephthalate or polypropylene. 6. The water-based ink for inkjet printing according to any one of claims 1 to 5 , wherein the pigment-containing polymer particles are crosslinked with a crosslinking agent. The water-based ink for inkjet printing according to any one of claims 1 to 6, which is for printing on flexible packaging or printing on labels and seals. An inkjet printing method, comprising printing on a low-absorbent print medium using the ink according to any one of claims 1 to 7.